Preparation of vinyl pyridines



Patented Sept. 23, 1952 'PREPAEATIONEF VINYL PYRIDINES JolmF-I. Hays,Wilmington, Del assignor tolHermules; Powder Company, Wilmington, illl acorporation of Delaware w. pjNdilrawing'. la plicationnu usm,1 4 YISceialNo. 7.65:,8017

' "This ilinvention. :relates rtorvinyl pyri'dineszzand.

more particularly,- :to" the 11 dehydrogenation Roi;

ethyl pyridines toagive 'rthe1v'eorrespondmg vinyl derivatives. Y

Various methods ihave been :suggestedsioraproducing vinyl pyridinesLbutithesemethods have been disadvantageous:inrthat axrelatively largenumber of steps were involved and .in' thatxlcw yields were obtained. Asa result, .suoh:methods did :not lend sufficient :simplicity :for:application to commercial use. As previously carried: {(1111} in theart, vinyl pyridines :usually. have :b'een. obtained by the condensationof formaldehydewith a :methyl pyridine i to produce the correspondingpyridyl ethanol. Such ta compound was then by passing the latter over:an active high itemperature dehydrogenation catalyst at temperaturesbetween about 450C. and about 0. This process is relatively f'ree "o'f-side-reacti'ons and after separation of the vinyl cor'npou'nd theunreac-ted ethyl pyridine may berecycl'ed; "thus giving a' continuousprocess for production of the vinyl pyridine.

In carryingoutthe process in accordance with this invention, an ethylpyridine, such as -ethy1- 2-methylpyridine, may be"'passedthrough-a hottube containing a high temperature dehydrogenation catalyst, 'such aschromium .oxide supported on alumina. The temperature may be maintainedin the neighborhood of 600 (3., and a .fiow rate of about 0.6 maybe-utilized. JSiibstantial conversion of the ethyl pyridine to thecorresponding vinyl compound will take place rapidly. Completeconversion or the ethyl pyridine-to the vinyl compound ordinarily doesnot take place, consequently the reaction products may be separated by.fractional distillation or crystallization or a combination of both.

T he following exampler constitutes "a cspecific embodiment oi theinvention. All parts given in the examplecrepresent parts by Weight.

The dehydrogenation apparatuswas of v the gravity feed type andconsisted of a spiralitube preheater leading-into a vertical iron tube;to

the lower end of which was attached an efiicient abubbler.

7 :2 Claims; omeo-.290)

2 c .multitube water-cooled condenser; The -catalyst tube contained athermocouple well iandlzwais charged. with a catalyst consisting of x121% ohm-- mium oxide on alumina. Nitrogencwas apassed slowly over. thecatalyst bed toflush .out any oxygen, and at the same time the catalyst..tube was .heated to .a temperature of; about 510 C. 5---ethyl2-methylpyridine was then passed through the hot apparatus .at a ratewhich produced .a steady stream -.of gas through an, exit A 'sampleofthetcrude reaction mix,- ture was analyzed .from time to time :todeter,- mine the amount of 2-methyl-5-vinylpyridine present. :A seriesof runs were .made using ,5 ethyl-2-methy1pyridine, the results @ofwhich-are found in .theifollowing stable. a

The seven reaction mixtures were combined .to vgive 1599 parts of-Haproduct which contained .16 22 methylsB-vinylpyridine as determined byhydrogenationanalysis. i

The :combined reaction mixture was charged .intoa distillationvesselwhich "was attached to a ZO pIate --g1ass helices-packed .fraotionationcolumn. The product then was subjected :to fractional -disti1lation,thetemperature at thev tcp of the column varying from about 62 C; toza-bout .86 C. .at-a pressure-of 28 to 29 mm. -.of-=mercury. Fourteen:separate fractions :were collected and theu'last three fractions:(boiling :points at 29 mm: :8l'.0" -85;6. rand -79;8-C., respectively;arefractive 'indices at (3.": t.1;5:1l9,;1=5316 :and 1.5413,respectively) were =crystallized and are-- (crystallized at atemperature of 60 from commercial pentane .{rom which theqmaterialboilingabove C. had beencremoved. En the final recrystallization; uponevaporating the excesspssolvent utilizing moderatevacuum, there wasobtained pure ZemethyI-B-Vinylpyridine. This :compound had :a melting.point xof; --"7-?v C.-, absorbed ;1-.65;% (theoretical 1.68%), hydrogenin the presence: of a palladium catalystandformed sa crystalline-picratewhich was "canary "yellow 111E010?! and .had amelting jpoint of160461516. Although: the example has :shown only-ethe :use

riineslarezoperable in'accordance with the process the5-ethyl-2-methylpyridine utilized in the example or such as 2,5-diethylpyridine. The process, in other words, is generally applicable to allalkyl pyridines in which at least one. of the alkyl substituents is anethyl group. The 5-ethyl-2-methylpyridine shown by the example maybe'made by the condensation of acetaldehyde, in the form of paraldehyde,with ammonia in the presence of glacial acetic acid. These reactants maybe heated for about 6 hours at 185 C. in an autoclave in order toproduce a reaction mixture which upon fractional distillation willafford a yield of about 65% of -5- ethyl-Z-inethylpyridine, based uponthe amount of acetaldehyde used.

The example has shown the use of chromium oxide supported on alumina asthe catalystfor the dehydrogenation process. Any other active hightemperature dehydrogenation catalyst known to the art may be used,however. From a consideration of chemical composition, the oxides oi thetransition metals of groups IV. V, and VI of the periodic table, such aschromium, molybdenum, tungsten, vanadium, titanium, zirconium, and thelike, are the best catalysts. Chromium oxide has been used mostextensively and the oxide is more active when supported on a carrier ofrelatively lower activity, such as alumina. Activated alumina alonepromotes dehydrogena tion but isless efiective than chromium oxide onalumina. The high adsorptive activity as well as the porous solidstructure of alumina constitutes the reason for its suitability.Relation of high adsorptive capacity to catalytic activity is evidencedby'the necessity of small amounts of water vapor, about 0.1 mole percent, in the reaction.

-' The temperature at which the reaction may be carried out. may bevaried from about 450 C. to about 800' C., although a preferable rangeis 'from about'550 C. to about 650 C. Aparticularly applicabletemperature range is from about 600 C. to about 630 C. The length oftime'necessary to eiiect conversion of the ethyl pyridine to thecorresponding vinyl compound will depend upon the rate at which theethyl pyridine passed through the reaction zone and upon the temperatureutilized. In general, substantial conversion to the vinyl compound maybe obtained utilizing a reaction temperature of 600 C. to 625 C. and aspace velocity (parts of feed mixture/part of catalyst/hour) of about0.5 to about 0.8.

Upon completion of the dehydrogenation process, the reaction mixture maybe treated in one of two ways or a combination of both in order toisolate the vinyl pyridine. Fractional distillation may be utilized, butthis requires a very efficient fractionating column and is somewhatdisadvantageous in that prolonged heating will 'causeconsiderable lossin reaction product due to formation of arubberlike residue.Crystallization from light petroleum naphtha, for example, at lowtemperatures also may be used to' isolate the vinyl pyridine. Thisprocedure is somewhat undesirable when large quantities of the reactionproduct are involved, however, consequently the most favorable procedureis a combination of fractional .distillation under reduced pressure andfractional crystallization. A rapid distillation may be used first ofall to concentrate the vinyl pyridine in certain fractions and thesefractions then may be dissolved in a solvent, such '4 as pentane, cooledto a temperature or about 30 C.'to about 70 C. to form the'pure vinylcompound by crystallization. Solvents other than pentane, such aspropane, butane, hexane, heptane. octane. nonane and decane, also may beused.- In general, any low boiling petroleum hydrocarbon solvent isoperable, the primary requisite for such a -solvent being that itmaintain its liquid state at the low temperatures used during thecrystallization.

'By the processor this invention, it is possible 'to produce the vinylpyridines more simply and economically than heretofore.

The process is relatively-free of side reactions and may be operatedcontinuously. The vinyl pyridines produc'ed by this process may be usedas monomers in the preparation of resins and synthetic rubbers. Theresinous materials prepared using vinyl pyridines are valuable for manypurposes since they contain a weakly basic nitrogen atom. The rubberlikematerials, such as the oopolymer of butadiene and2-methyl-5-vinylpyridine, have many characteristics which render themuseful in various fields.

What I claim and desire to protect by Letters Patent is:

1. The process of preparing a vinyl substituted pyridine compound whichcomprises passing an ethyl substituted pyridine over an active hightemperature dehydrogenation catalyst at a temperature between about 450C. and about 800 C., and fractionally crystallizing the resultingreaction mixture comprising the vinyl substituted pyridine compoundand'the unchanged ethyl substituted pyridine compound from a low boilingpetroleum hydrocarbon solvent at a temperature between about 30 C. andabout '70 C.

2; The process of preparing a'vinyl substituted pyridine compound whichcomprises passing an ethyl substituted pyridine over an active hightemperature dehydrogenation catalyst at a temperature between about 450C. and about 800 C., fractionally distilling the resulting reactionmixture comprising the vinyl substituted pyridine compound and theunchanged ethyl substituted pyridine compound, and fractionallycrystallizing the distillation fractions rich in the vinyl sub.-stituted pyridine compound from a low boiling petroleum hydrocarbonsolvent at a temperature between about -30 C. and about 70 C.

. JOHN T. HAYS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,141,611 Malishev Dec. 27, 19382,300,971 Roberts Nov. 3, 1942 2,376,532 Egloff May 22, 1945 2,376,709Mattox May 22, 1945 2,402,158 Glowacki June 18, 1946 FOREIGN PATENTSNumber Country Date 849,126 France 1939 115,967 I Australia Sept. 1942132,042 Austria Feb. 1935 OTHER. REFERENCES Berichte, 20 (1887), p.1643.

J. Amer; Chem. $00., May 1942, pp. 1093 and Degering: Organic NitrogenCompounds, 1945, p. 628.

1. THE PROCESS OF PREPARING A VINYL SUBSTITUTED PYRIDINE COMPOUND WHICHCOMPRISES PASSING AN ETHYL SUBSTITUTED PYRIDINE OVER AN ACTIVE HIGHTEMPERATURE DEHYDROGENATION CATALYST AT A TEMPERATURE BETWEEN ABOUT 450*C. AND ABOUT 800* C., AND FRACTIONALLY CRYSTALLIZING THE RESULTINGREACTION MIXTURE COMPRISING THE VINYL SUBSTITUTED PYRIDINE COMPOUND ANDTHE UNCHANGED ETHYL SUBSTITUTED PYRIDINE COMPOUND FROM A LOW BOILINGPETROLEUM HYDROCARBON SOLVENT AT A TEMPERATURE BETWEEN ABOUT -30* C. ANDABOUT -70* C.